The use of laminated plastic materials to form armor structure is old as evidenced by the disclosures in a number of U.S. patents, including the following U.S. Pat. Nos. 3,179,553; 3,539,442; 3,573,150; 3,577,836; 3,657,057; and 3,722,355. While these references utilize different types of plastic materials in the structures thereof, they do not teach or suggest the use of plastic laminates of substantially different densities for the purpose of causing delaminations at the interfaces of adjacent laminates. Such delamination is effective in dissipating the kinetic energy of a projectile striking and entering a structure comprised of such laminates.
A number of groups of laminates of different densities have been used in the past but such use has always required that these groups be parts of a larger armor unit having additional layers of foam or other materials bonded to and disposed between adjacent pairs of laminate groups. Thus, such armor unit is extremely bulky and heavy, and is not practical for many applications. Until the present time, it was believed that this construction required the presence of such additional layers; however, it has now been established that a laminate group of the aforesaid type can, by itself, be used as armor structure without the need of layers of foam or any other material on the outer faces thereof. This permits armor structure to be made from only a single group of laminates of different densities and allows the armor structure to be of limited size and weight yet it can be highly efficient by itself in stopping high-speed projectiles without affecting its structural integrity, thereby eliminating the need for additional structure, such as outer layers of foam, ceramic or metal, as has been utilized in the prior art.
Another drawback of the armor structures of the prior art is that they are formed of materials which are easily shattered when a relatively few projectiles are shot into the same. The materials forming the prior structures are not sufficient to avoid such structural damage. Thus, the structures must be frequently replaced if they are to be used as protection over a relatively long period of time.